Expansion tank with membrane thermal protection

ABSTRACT

An expansion tank for accommodating hot expanded fluid in a heat transfer fluid system has a tank body defining an internal volume. A fluid inlet is provided on the tank body for connection to the heat transfer fluid system. A membrane, such as a diaphragm or a bladder, divides the internal volume into first and second sections. The first section includes a buffer zone between the fluid inlet and the membrane. The buffer zone contains a predetermined volume of tempering fluid for cooling down the incoming hot expanded fluid at its entry in the expansion tank. The buffer zone has an air valve for venting air from the buffer zone while the buffer zone is being filled up with the tempering fluid. The second section on the opposed side of the membrane is maintained under pressure with a gas.

RELATED APPLICATIONS

The present application claims priority on U.S. provisional patentapplication No. 61/583,329 filed on Jan. 5, 2012, the entire content ofwhich is herein incorporated by reference.

TECHNICAL FIELD

The application relates generally to heat transfer fluid systems and,more particularly, to expansion tanks suited for use in such systems.

BACKGROUND OF THE ART

It is well know to use expansion tanks in closed looped heat transferfluid systems to accommodate increases in volume resulting from thetemperature rise of non-compressible heating fluids, such as water,glycol, glycerine and propylene glycol solutions. Such expansion tanksallow controlling the system operating pressure by providing to theexpanded heating fluid a place to go.

Commercially available expansion tanks typically comprises twohalf-shell members adapted to be assembled together to define aninternal volume. A membrane, which may be provided in the form of adiaphragm or a bladder, divides the internal volume of the tank in twosections. A first section of the tank has a heating fluid inletconnected to the pipe network of the system for accommodating the extravolume of heating fluid created by thermal expansion. The second sectionof the tank, sometimes referred to as the dry side, contains acompressible gas (e.g. air) under pressure. When the heating fluid isheated, it expands. The expended heating fluid enters the first sectionof the expansion tank. As the heating fluid pressure increases, itpushes the internal membrane against the pressurized gas on the dry sideof the membrane, thereby compressing the gas.

When such an expansion tank is used in a high temperature system, suchas a solar heating system, the heating fluid may reach temperatureswhich are potentially higher than the maximum temperature that can bewithstood by the membrane. This may result in damages to and prematurewear of the membrane.

Therefore, there is a need to provide a new expansion tank arrangementwherein the internal membrane of the tank is protected from beingexposed to temperatures which exceed the temperatures that can bewithstood by the membrane.

SUMMARY

It is therefore an object to protect the membrane of an expansion tankfrom being damaged as a result of being exposed to excessivetemperatures.

In one aspect, there is provided an expansion tank for accommodating hotexpanded fluid in a heat transfer fluid system. The expansion tankcomprises a tank body having an internal volume, a fluid inlet providedon the tank body and adapted to be connected to the heat transfer fluidsystem, a membrane for dividing said internal volume into first andsecond sections, said first section including a buffer zone between thefluid inlet and the membrane, the buffer zone containing a predeterminedvolume of tempering fluid for cooling down any incoming hot expandedfluid at its entry in the expansion tank, the buffer zone having an airvalve for venting air from the buffer zone while the buffer zone isbeing filled up with the tempering fluid, the second section on theopposed side of the membrane being filled up with a pressurized fluid,the second section of the internal volume having a valve for allowingthe second section to be maintained at a predetermined pressure.

In a second aspect, there is provided an expansion tank for use in aheat transfer fluid system, the expansion tank comprising a shelldefining an internal volume, a membrane dividing said internal volumeinto a gas chamber and an expandable fluid receiving chamber, a fluidopening provided on said shell and communicating with said expandablefluid receiving chamber, a closable gas inlet provided on said shell andcommunicating with said gas chamber for allowing a pressurized gas to bedirected and maintained under pressure in said gas chamber, a shellextension member mounted over one end of the shell to define therewith athermal buffer chamber adapted to be filled with a tempering fluid, saidthermal buffer chamber communicating with said expandable fluidreceiving chamber via said fluid opening, an air valve provided on saidshell extension member to allow air to be expelled from the thermalbuffer chamber while the same is being filled up with the temperingfluid, and an inlet port provided on the shell extension member andconnectable to the heat transfer fluid system, the thermal buffer beingdisposed between the inlet port and the fluid opening of the first shellmember, whereby hot expanded fluid from the system mixes with thetempering fluid contained in the thermal buffer chamber at its entry inthe expansion tank, the hot expanded fluid being cooled down by thetempering fluid.

In accordance with a still further general aspect, there is provided anexpansion tank suitable for any heat transfer fluid system, filled or tobe filled with potable water, glycol, a mix of water and glycol, orelse. The tank can be of any volume and its construction can be ofmetal, plastic or equivalent and its finish may be epoxy paint,electrostatic paint powder, regular paint, or equivalent. The tank mayhave a Schrader-type valve or a ball valve to let air out of a firstbuffer section thereof when the same is being filled with a tempered orcooling fluid. The volume of the first buffer section is determined as afunction of the fluid temperature, the volume being bigger whentemperature is higher and smaller when the temperature is lower. Heatexchange promoting structures, such as metal fins, may be provided onthe first section of the tank to more efficiently release heat from the“cooling” fluid filling the first section of the tank. The first sectionmay also be provided with a diffuser adapted to be connected to theheating system for homogeneously diffusing any hot expanded fluid comingfrom the system into the tempered cooling fluid present in the firstsection of the expansion tank. In the first section, the hot expandedfluid mixes with the tempered fluid and is thus cool down to anacceptable temperature. The tank has a second section connected in fluidflow communication with the first section to receive the cooled expandedfluid. The second section is separated from a third section by amembrane, such as a bladder, a diaphragm or a bladder-type diaphragm,which may be made of EPDM, butyl or any equivalent material. The thirdsection contains a pressurized gas against which the membrane maydeflect to accommodate the expanded fluid. The third section is providedwith a Schrader-type valve, a ball valve or any other suitable valve topre-charge the expansion tank at a desired pressure.

Further details of these and other aspects of the present invention willbe apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures, in which:

FIG. 1 is a partial cross-section of an expansion tank in accordancewith an embodiment of the present invention; and

FIGS. 2 a to 2 c are cross-section views illustrating the installationand the operation of the expansion tank shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 illustrates an expansion tank 10 suited for use with hightemperature fluid heating systems, such as solar heating systems. Theexpansion tank 10 is configured to accommodate the expansion of thefluid in the system when the same is heated. The expansion tank 10provides a place for the expanded fluid to go. The fluid may be water,glycol, a mixture of water and glycol or any other fluids that may beused in a heating system.

The expansion tank 10 generally comprises first and second half-shellmembers 12 and 14 assembled together such as by welding or othersuitable techniques. The first and second shell members 12 and 14 mayform a generally cylindrical housing. The shell members 12 and 14 may bemade out of plastic, metal or any suitable materials. The first andsecond shell members 12 and 14 define therebetween an internal volume ofthe expansion tank 10. As known in the art, a flexible elastomericmembrane 16 divides the internal volume of the expansion tank 10 into aheating fluid chamber 18 and a pressurized gas chamber 20. According tothe illustrated embodiment, the flexible membrane 16 is provided in theform of a bladder. However, it is understood that the membrane couldtake various forms. For instance, it could consist of an elastomericdiaphragm. According to the illustrated embodiment, the bladder 16 maybe made out of rubber, EPDM, butyl or other suitable materials. As shownin FIG. 1, the bladder 16 may me mounted at one end thereof to amounting flange 22 surrounding a central inlet hole 24 defined in theend wall of the first shell member 12. Bolts 26 or other suitablefasteners may be used to removably install the bladder 16 in theinternal volume of the expansion tank. The bladder 16 could also bepermanently attached to the first shell member 12. A valve 28 is mountedto the opposed end wall of the second shell member 14 of the tank 10 forallowing the gas chamber 20 to be filled with a gas under pressure. Thevalve 28 could be provided in the form of a Schrader-type valve or aball valve. It is understood that other types of valves could be used aswell. A cap 30 may be provided on the outer surface of the end wall ofthe second shell member 14 to protect the valve 28.

In order to prevent the expanded fluid from coming into direct contactwith the bladder 16, it is herein proposed to install a third shellmember 32 over the first shell member 12 to form therewith a bufferchamber 34 adapted to be filled with a “cooling” fluid that will mixwith the incoming hot expanded fluid and thus cool the same to atemperature which is below the temperature that the can be withstand bythe bladder 16. The third shell member 32 can be viewed as an extensionshell member into which the cylindrical housing of the tank is nested.The third shell member 32 can be welded or otherwise suitably joined tothe first shell member 12.

As shown in FIG. 1, an air valve 36 is provided on the end wall of thethird shell member 32 for venting air from the buffer chamber 34 whilethe same is being filled up with the cooling fluid. The cooling fluidmay be the same fluid as in the heat transfer system but maintained at alower temperature, typically at room temperature. In some applications,the cooling fluid could be different from the heating fluid of thesystem in which the expansion tank is installed. The temperature andvolume of cooling fluid is selected to provide a generally temperedfluid body which will effectively lower the temperature of the hotexpanded fluid which intermittently flows into the expansion tank 10 toa temperature which is below the maximum temperature that the bladder 16can withstand. Accordingly, the sizing of the buffer chamber 34 isfunction of the temperature of the expanded fluid and of the volume ofexpanded fluid to be accommodated in the fluid chamber 18. Heatpromoting structures (not shown), such as fins, may be provided on theouter surface of the third shell member 32 to accelerate the release ofheat from the body of fluid contained in the buffer chamber 34.

A fluid inlet 38 adapted to be connected to the fluid heating system isprovided on the end wall of the third shell member 32. The fluid inlet38 may include a diffuser 40 to uniformly diffuse the incoming hotexpanded fluid into the body of cooling fluid contained in the bufferchamber 34. A fitting or connector 42 is provided at the outer distalend of the diffuser 40 for connection with a mating connector mounted ina line of the system. The diffuser 40 may be removably bolted or weldedon a mounting flange 44 surrounding the inlet 38 of the third shellmember 32. In this way, the diffuser 40 and the connector 42 may bereadily removed to provide easy access to the bladder 16 and the flange26 to which it is mounted. However, it is understood that the wholeassembly could be welded to provide a permanently attached diaphragm anda fixed buffer chamber with a welded connection; no part beingremovable.

Referring now to FIGS. 2 a to 2 c, we will now describe the installationand operation of the expansion tank 10. First, the expansion tank 10 isconnected via connector 42 to the piping network N of the system asshown in FIG. 2 a. The valve 28 at the bottom end of the second shell 14is connected to a source of pressurized gas (e.g. air) and is thenopened to pressurize the gas chamber 20 to a predetermined pressure.Once the desired pressure is reached, the valve 28 is closed. In thisinitial stage of the installation, the bladder 16 is in a collapsedstate as shown in FIG. 2 a. Thereafter, the piping network N of thesystem is filled with the heating fluid (e.g. glycol solution) asschematically depicted by the dash lines in FIG. 2 a. The fillingoperation of the piping network N is typically carried on at roomtemperature.

The air valve 36 provided at the top of the buffer chamber 34 is openedto allow air to be expelled out of the buffer chamber 34 and to, thus,allow ingress of the tempered heating fluid into the buffer chamber 34.The tempered fluid present in the buffer chamber 34 as schematicallydepicted in FIG. 2 b, will serve as a body of cooling fluid to cool downany incoming hot expanded fluid at its entry in the expansion tank 10.The pressure exerted by the pressurized gas in the gas chamber 20against the bladder 16 maintains the bladder in its collapsed stateduring the filling operation of the buffer chamber 34, therebypreventing the tempered fluid from flowing into the bladder 16. Once thebuffer chamber 34 has been full up, the air valve 36 is closed.

The system may then be operated. In use, when the heating fluid isheated, it expands and the expanded fluid flows into the expansion tank10, thereby causing the bladder 16 to inflate in order to accommodatethe expansion of the fluid in the system. At its entry in the expansiontank 10, the hot expanded fluid is cooled down by the cooling fluidalready present in the buffer chamber 34. The hot expanded fluid iscooled down to a temperature which is inferior to the limit temperaturethat can be sustained by the bladder. The buffer chamber 34 thus allowsprotecting the bladder from being exposed to excessive temperature.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the first and second shells could for instance be replacedby a one-piece hollow container body. Such a one-piece constructioncontainer body could be blow molded. Also it is understood that whilethe buffer chamber as been shown as being provided at the upper end ofthe tank, the expansion tank could be installed upside down with thebuffer chamber at the bottom of the tank. It is understood that in suchan inverted installation, the air valve 36 would be repositioned such asto remain at the upper end of the buffer chamber. Still othermodifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

What is claimed is:
 1. An expansion tank for accommodating hot expandedfluid in a heat transfer fluid system, the expansion tank comprising atank body having an internal volume, a fluid inlet provided on the tankbody and adapted to be connected to the heat transfer fluid system, amembrane mounted within said tank body for dividing said internal volumeinto first and second sections, said first section including a bufferzone between the fluid inlet and the membrane, the buffer zonecontaining a predetermined volume of tempering fluid for cooling downany incoming hot expanded fluid at its entry in the expansion tank, thebuffer zone having an air valve provided at an upper end thereof forventing air from the buffer zone while the buffer zone is being filledup with the tempering fluid, the second section on the opposed side ofthe membrane being filled up with a pressurized fluid, the secondsection of the internal volume having a valve for allowing the secondsection to be maintained at a predetermined pressure.
 2. The expansiontank defined in claim 1, wherein the tank body comprises first andsecond shell members, each of said first and second shell members havingan end wall and a tubular side wall, said first and second shell membersbeing assembled together with respective end walls in opposed facingrelationship, and wherein the tank body further comprises a third shellmember installed over said first shell member, said buffer zone beingdefined between said third and first shell members, the second sectionof the internal volume being bounded by the membrane, the first shelland the second shell.
 3. The expansion tank defined in claim 2, whereinthe fluid inlet and the air valve are both provided on said third shellmember, and wherein the membrane is provided in the form of a bladdermounted in an inlet hole defined in the end wall of the first shellmember, the bladder being in fluid flow communication with the bufferzone and expandable in the second section of the internal volume betweenthe first and second shell members.
 4. The expansion tank defined inclaim 2, wherein the valve for maintaining the second section at apredetermined pressure is mounted to one of the first and second shellmembers.
 5. The expansion tank defined in claim 1, wherein the fluidinlet includes a diffuser for diffusing incoming hot expanded fluid intothe tempering fluid contained in the buffer zone.
 6. The expansion tankdefined in claim 1, wherein the tank body comprises a generallycylindrical housing having a side wall and opposed end walls, and ashell member having one end wall and a side wall extending from the endwall, the shell member being mounted over the housing, the buffer zonebeing defined between the shell member and the housing, the membranebeing mounted within the housing and communicating with the buffer zonevia an opening defined in one of the end walls of the housing.
 7. Anexpansion tank for use in a heat transfer fluid system, the expansiontank comprising a shell defining an internal volume, a membrane dividingsaid internal volume into a gas chamber and an expandable fluidreceiving chamber, a fluid opening provided on said shell andcommunicating with said expandable fluid receiving chamber, a closablegas inlet provided on said shell and communicating with said gas chamberfor allowing a pressurized gas to be directed and maintained underpressure in said gas chamber, a shell extension member mounted over oneend of the shell to define therewith a thermal buffer chamber adapted tobe filled with a tempering fluid, said thermal buffer chambercommunicating with said expandable fluid receiving chamber via saidfluid opening, an air valve provided on said shell extension member toallow air to be expelled from the thermal buffer chamber while the sameis being filled up with the tempering fluid, and an inlet port providedon the shell extension member and connectable to the heat transfer fluidsystem, the thermal buffer being disposed between the inlet port and thefluid opening of the first shell member, whereby hot expanded fluid fromthe system mixes with the tempering fluid contained in the thermalbuffer chamber at its entry in the expansion tank, the hot expandedfluid being cooled down by the tempering fluid.
 8. The expansion tankdefined in claim 7, wherein the volume of the thermal buffer section issufficient to cool down the hot expanded fluid to a temperature which isinferior to a maximum temperature that the membrane is able towithstand.
 9. The expansion tank defined in claim 7, wherein the shellcomprises first and second shell members, each of said first and secondshell members having an end wall and a tubular side wall, the first andsecond shell members being assembled together with respective end wallsin opposed facing relationship.
 10. The expansion tank defined in claim9, wherein the fluid opening is defined in the end wall of the firstshell member, and wherein the shell extension member is mounted over thefirst shell member.
 11. The expansion thank defined in claim 7, whereinthe air valve is disposed at an upper end of the thermal buffer chamber.12. The expansion tank defined in claim 7, wherein the fluid inletincludes a diffuser for diffusing incoming hot expanded fluid into thethermal buffer chamber.
 13. The expansion tank defined in claim 7,wherein the membrane is provided in the form of a bladder extending fromsaid fluid opening, the bladder being in fluid flow communication withthe thermal buffer chamber.